Current methods that utilize an on site bioswale technique are highly inefficient and tend to rapidly become ineffective due to deferred maintenance and other issues. To illustrate this point, it is helpful to understand how a typical bioswale functions in order to treat contaminated water.
During a storm event, rain falls on urban development that is composed of approximately 70% impermeable surfaces (paving, roads, buildings, etc.) and 30% permeable surfaces (grasses, shrubs, and landscapes in general). These surfaces, especially the impermeable ones, are heavily laden with contaminants such as hydrocarbons, metals, bacteria, nitrogen, phosphorous nutrients, silt, debris, herbicides, insecticides, and pesticides. Currently, rain washes these surfaces directly into municipal stormwater management systems where it ends up fouling waterways and oceans. One method of removing these various contaminants is to channel the contaminated water into a landscaped structure commonly known as a bioswale.
With more urban development has come more regulation. In the past 20 years; laws have been passed requiring that runoff from paved areas drain into adjacent landscape bioswales where it is mitigated by soil and plant biology, allowing some of it to infiltrate soils and most of it to drain to municipal stormwater management systems. A typical bioswale is a vegetated depression in the landscape that channelizes stormwater for filtration of contaminants prior to drainage into the municipal stormwater system. This setup poses some serious problems however, as discussed below.
The typical bioswale requires an extraordinary amount of maintenance to maintain its effectiveness at removing contaminants from stormwater. Over the course of many rainfalls, the bioswale fills with heavily polluted silts that cause the bioswale's biological system, primarily soil biology and vegetation, to fail. To adequately maintain the bioswale, it is required that the polluted silts be removed from the bioswale once or twice per year. This is a very expensive and labor intensive process, and usually consists of removing the top 1″-2″ of soil and vegetation from the entire length of the bioswale. It may also be necessary to modify the irrigation system. Other issues related to this burdensome process include soil preparation, revegetation, and disposal of polluted debris. In other words, the bioswale has to be rebuilt periodically to maintain its effectiveness. Few bioswales are maintained to this level. However, stormwater quality legislation requires that many current and future bioswales be adequately maintained for effectiveness. Thus there is a need in the art for a high performance modular bioswale system for treatment of runoff water that is highly effective yet relatively easy to construct and maintain. It is to these ends that the embodiments of the invention have been developed.